Remote-reading specific-gravity indicator



1944. J. WQODBRIDGE 2,354,847

REMOTE READING SPECIFIC GRAVITY INDICATOR Filed Oct. 25, 1940 l\llllllll5 I I I I l 1 I I.

' a 65 AffUR/Vf)? connecting tube.

Patented Aug. 1, 1944 Rumors-ammo. SPECIFIC-GRAVITY mmca'roa JosephLester Woodbrid ge, Philadelphia, Pa., as-

signor to The Electric Storage Battery Company, Philadelphia, Pa., acorporation of New Jersey Application October 25,1940, Serial No.362,769

3 Claims.

The apparatus is designed to indicate the specific gravity of a liquidin a suitable container at a point at some distance from the container.It consists generally in two inverted cup-shaped vessels or air bellslocated one above the other in the vessel and submerged in the liquidwhose specific gravity is to be measured. These cups are open below toprovide access to the liquid which rises to a certain level in the cups,the space above that level being filled with gas whose pressure istransmitted by suitable small bore tubing to th indicating apparatus.This indicating apparatus consists in two corresponding receptacles, orbulbs, one above the other, con- 'nectedatthe lower ends by a straighttubeof I comparatively small bore and at their upper ends Y to the'tubing from the corresponding cups in the v'esseL The receptacles in theindicating appa- 35 ra'tus' are partially filled with'a suitable liquid.which also fills the small bore tubing connected I to their lower ends.This latter tubing is transparent, and intermediate of its length thereis a short section of liquid of a different color from and nonmisciblewith the liquid which fills the balance of the tube and whose positionin the tube is indicated on an indicatingscale adjacent to the tube.Variations in the specific gravity of the liquid in the vessel willintroduce changes in the gas pressure in the connecting tubing, causingliquid to be transferred from the lower bulb through the indicatingtubing to the upper bulb or vice versa, this transfer being indicated bya shifting of the colored section of liquid in the The invention will bemore clearly understood by reference to the accompanying drawing inwhich the single figure is a diagrammaticview illust ating features ofthe invention.

Referring to the drawing, l is the vessel containing the liquid 2, whosespecific gravity is to be indicated. The upper level of the liquid isshown at 3. Immersed in the liquid are two in. verted cup-shapedreceptacles or air bells 4 and 5 one located directly above the otherand provided at the bottom with openings 6 and I, respectively,affording access from the liquid to the interior of the cup. This liquidwill risein the cups to the level indicated by the lines 8 and 9,

. respectively-being prevented from rising further by the presence ofthe gas or air in the space above. The cup 4 is connected by means ofthe pressure tube I to the upper end of th bulb I I of thepressure-indicating apparatus while the cup is connected by. means ofthe pressure tube I! with the upper end of the bulb l3 of the presabovenormal atmospheric sition as indicated by an sure-indicating apparatus.The lower end or the bulb l I is connected with the lower end of thebulb l3 by the straight small bore indicating tube or column l4, andthis tube together with the lower portions of the bulbs II and I3 isfilled with a liquid l5 which rises in the two bulbs to the levelsindicated by the lines It and I1, respectively. The upper portions ofthe cups 4 and 5 and the upper portions of the bulbs II and I3 togetherwith the pressure tubes l0 and I2 are filled with a gas such as airwhich may be slightly pressure.

At an intermediate point in the indicating tube I4 is a small section ofliquid I 8 of a difierent color from that of the balance of the liquidso that its position in the tube can be clearly seen, the tube beingtransparent. This liquid I8 is preferablyof about the same specificgravity as the balance of the liquid in the tube and is nonmiscible withit.

If the specific gravity of the liquid IS in the indicating tube andbulbs is the same as that of the liquid 2 in the vessel I, equilibriumwill be established when the difference in head between the level It inthe bulb II and the level I1 in the bulb I3 is the same as thedifierence in head between the level 8 in the cup 4 and the level 9 incup 5. If new the specific gravity of th liquid 2 in vessel I should,for example, increase, this equilibrium will be disturbed and, in orderto reestablish equilibrium, the head between the level I 6 and the levelI! must be increased so that the weight of the column of the'liquid I5corresponding to the new distance between levels [6 and I1 will be equalto the weightof a corresponding column of liquid between the levels 8and 9 at the increased specific gravity. To reestablish thisequilibrium, liquid will be forced down from the vessel l3 and upthrough the tube l4 into the vessel II. This transfer will move theindicator l8 upward in the tube to a new poappropriate scale l9 adjacentto the tube. The change in the levels It and I1 may be comparativelysmall but this will be magnified in the proportion between the'area ofthe bore of the tube l4 and the cross-sectional area of the bulbs l land I3 so that an accurate reading of the change in specific gravity ofthe liquid may be obtained.

This apparatus may be employed in various applicationsfor reading thespecific gravity of liquids and would be particularly useful for readingthe specific gravity of the electrolyte in a storage battery cell. Forsuch an application, the inverted conical baiiies20 and 2| are shownlocated beneath the cups 4 and 5, respectively, to divert the bubbles ofgas which are frequently evolved in the cell and prevent them fromentering the cups and thus changing the volume of gas in the cups,pressure tubes and bulbs.

In order to more clearly illustrate the performance of this apparatus, anumerical example will now be given covering the application to the cellof a storage battery. It will be assumed that the specific gravity ofthe electrolyte in the cell may vary from 1.100 to 1.250, resulting in arange of $0.075 on either side of the mean value of 1.175.

The vertical distance between the levels 8 and 9 in the cups 4 and istaken as 6" when the specific gravity of the liquid is at the mean valueof 1.175. The internal diameter of the cylindrical cups 4 and 5 is 1".The diameter of the bore of the pressure tubes and I2 is 0.04" and thelength of the horizontal portions of these tubes is approximately 10feet. The internal diameter of the bulbs H and i3 is 0.35" and theheight of these bulbs is 1.0". The bore of the indicating tube i4 is0.1". Assuming the specific gravity of the liquid IS in the bulbs andindicating tube to be 1.175, the equilibrium will be established asindicated in the figure when the distance between the levels 8' and 9 isequal to the distance between the levels It and II, that is 6".

Assume now that the specific gravity of the liquid 2 increases to 1.250.The weight of the 6" column of liquid between the levels 8 and 9 will beincreased in the ratio of 1.175 to 1.250, that is 1.0638. To balancethis increase of head. the head in the indicating column and bulbs mustbe increased in the same ratio. that is from 6" to 6.3828", 1. e., thelevel in the lower bulb l3 must be reduced by 0.1914" and that in theupper bulb H must be raised by the same amount. The volume of liquidthus transferred from the lower to the upper bulb through the indicatingtube 14 will be 0.1914 multiplied by the area of the internalcross-section of the bulb, which is (0.35) 0.7854, or 0.0184 cubicinches. This transfer w ll cause the indicator l8 to travel a distanceequal to this volume divided by the area of the bore of the tube, i. e.,0.0184/0.007854 or 2.34". The full length of the scale is will then be4.68" to cover the complete range from 1.100 to 1.250 specific gravity.This will provide a suillciently open scale for accurate readings.

The apparatus as above described will ive accurate readings. of thespecific gravity of the electrolyte provided the tem erature and thelevel 3 remain constant. The effect of changes of level of theelectrolyte within the usual limits in practice will not appreciablyaffect the readings indicated by this apparatus.

In regard to temperature, it is usually desirable that -the indicationof specific gravity be automatically corrected for variations oftemperature. The apparatus disclosed herein provides this automatictemperature correction bv includin a greater volume of gas in the cup 5above the level 9 than that in the cup 4 above the level 8. Thus. if thetemperature should increase. the volume of gas in these cups willincrease but this increase in the cup 5 will be reater than that in thecup 4, thus increasin the head between the level 8 and the level 9. Thisdifierence in volume of gas can be made such that the increase in headwill counteract the decrease in specific gravity due to the increase intemperature of the electrolyte.

To illustrate thisin the numerical example,

assume a change in temperature from 25 C.- 9

60 C. This will reduce the actual specific gravity from 1.175 to 1.154.To compensate for this, the head between level 8 and level 9 must beincreased in the same ratio, from 6" to 6.11". This change oftemperature will increase the volume of gas in each cup by and, sincethe two cups have the same diameter, the volume will vary as the heightof the gas space. Hence, representing these heights by I and herespectively we have from which 0.11 hi h4]- -0.94 and the height of thegas space in cup 5 should be 0.94" more than that in cup 4.

It will be understood that modifications in the details of the apparatusmay be made without departing from the spirit of the invention. Thespecific gravity of the liquid in the indicating tube and bulbs need notbe the same as that in the vessel I provided the distance between thelevels l8 and I1 is correspondingly changed. If, in the case of thestorage battery cell, the bai'iles 20 and 2| are omitted, the cups 4 and5 will fill with gas, bringing the levels 8 and 9 down to the lower rimsof the cups which will eliminate the provision for temperaturecorrection.

While I have shown the cups 4 and 5 and the bulbs Ii and 13 located inthe same vertical line, one above the other, this arrangement would notbe necessary if the apparatus is so installed that there will be notilting through a vertical angle.

If the apparatus is assembled as shown in the drawing with the cups 4and 5 and the bulbs II and I3 vertically aligned, a considerable amountof tilting can take place without seriously affecting the accuracy ofthe indication if both parts of the apparatus always tilt by the sameamount as would be the case if the entire apparatus is installed on anelectric locomotive or a ship.

Instead of the short section of colored liquid ll, any other index maybe provided to show the movement of the liquid column in response tochanges in specific gravity.

It will be noted that the walls of the bells are imperforate to opposeescape of gas over the complete range of level.

It will be obvious to those skilled in the art that modifications may bemade in details of construction and in matters of mere form withoutdeparting from the spirit of the invention.

I claim:

1. In apparatus for indicating the specific gravity of a liquid, thecombination of two hollow vessels immersed in the liquid at diflerentlevels, each vessel having an opening in the bottom thereof andpartially filled through said opening by said liquid but closed to theliquid above said opening, a specific gravity indicating devicecomprising two hollow bulbs located at difierent levels and connected attheir lower ends by an indicating tube, transparent over at least a partof its length and of smaller internal cross-section than that of thebulbs, a pressure tube connecting the space above the liquid in theuppermost vessel with the upper space in the uppermost bulb, anotherpressure tube connecting the space above the liquid in the lowermostvessel with the upper space in the lowermost bulb, a liquid filling theindicating tube and the lower spaces of the two bulbs of which a sectionis of a diiferent color from the rest and is located in a transparentportion of the indicating tube, and gas filling the pressure tubes andthe upper spaces in the vessels and the bulbs but insumcient in volumeto displace the liquid rislng into the lower spaces of the vessels.

2. In apparatus for indicating the specific gravity of a liquid. thecombination of two hollow vessels immersed in the liquid at difierentlevels, each open below to give access to the liquid but closed to theliquid above, a specific gravity indicating device comprising two hollowbulbs located at different levels and connected at their lower ends byan indicating tube, transparent greater than that in the uppermostvessel .where-. by compensation for the eflectsof changes of temperatureof the first-mentioned liquid on its specific ravity is efi'ected. 3.Apparatus for indicating the specific grav ity of a liquid comprising aninverted cup shaped vessel adapted to be immersed in the upper portionoi a quantity of liquid the specific gravity of which is to beindicated, a second inverted cup shaped member having a height greaterthan said first cup shaped member adapted to be im-" mersed in the lowerportion 01' a said quantity of liquid, each of said cup shaped membershaving an opening at the lower end thereof whereby said vessels'arepartially filled through said'opening by said liquid, 9. dill'erentialpressure indicating device, pressure tubes connecting the spaces abovethe liquid level in each 01 said members with said indicating device,and a gas filling the pressure tubes and the spaces above the liquid ineach of said members but insufiicient in volume to displace the liquidrising in the lower portions thereof, said difierence in height betweensaid lower and upper members providing for gas spaces havingsubstantially diflerent heights thereby providing means for compensatingfor the pressure tubes and the upper -srmces in the vessels and thebulbs, the height of the gas-filled space in the lowermost vessel beingsubstantially 80 the efifects of changes in the temperature of saidquantity of liquid on its specific gravity.

JOSEPH LESTER WOODBRIDGE.

